The influence of geographical area of production and nitrogenous fertiliser on yields and quality parameters of clonal tea

Abstract

Variations in requirements for tea production in Kenya and factors controlling growth and production of secondary metabolites responsible for the quality parameters are indicative of the need for non-uniform recommendations. Nitrogen is the main nutrient for which tea shows easily demonstrable yield and quality responses. Fertilizer applications at rates between 100 and 250 kg N/ha/year of NPKS 25:5:5:5 are currently recommended in tea production. Although yield and black tea quality variations with nitrogen rates had been observed in the past, the studies were at single geographical locations. Where comparisons were done at different locations, the genotypes were different making it impossible to isolate environmental and genotypic effects. The response of single genotype to varying rates of nitrogen in the major tea growing areas has not been reported. Consequently, it is not known if the recommended nitrogen rates are optimal in all tea growing areas for production of high yields and good quality black teas. Trials were conducted in five major tea growing regions of Kenya to quantify the yields and illustrate plain tea quality parameters responses of cultivar BBK 35 to varying rates of NPKS 25:5:5:5 fertiliser applied at 0, 75, 150, 225 and 300 kg N/ha/year. Yields were recorded for a period of ten years (1998 to 2007). Pluckable shoots from the plots were processed into black tea and analyses for quality carried out in 2007. Yields significantly (P < 0.05) increased while quality declined with increasing rates of nitrogen. The mean yield varied in the following order: Sotik Highlands > Changoi > Karirana > Kipkebe > Timbilil. Also plain black tea quality as measured by theaflavins, thearubigins, total colour, brightness and sensory evaluations varied with geographical area of production. The theaflavins declined in the order: Changoi > Karirana > Timbilil > Kipkebe > Sotik Highlands. There was significant (P ≤ 0.05) interaction between geographical area of production and nitrogen fertilizer rates in yields demonstrating that yield response of BBK 35 to nitrogen varies with localities. The actual optimal nitrogen for the individual locations, however, will also be affected by quality, cost of production including cost of fertilisers and realised tea prices. Location specific recommendations need to be developed to promote high yields and production of high quality black teas in the different tea growing regions.